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Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region
CJAI 05, February 19, 2008
doi: 10.3752/cjai.2008.05

Matthias Buck, Stephen A. Marshall, and David K.B. Cheung

Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1

 

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77. Polistes fuscatus (Fabricius, 1793)
Figs B1.3, 7; B10.7, 11, 23, 25, 26, 28, 33, 34, 39, 41, 42, 54–57; C77.1–15.

Polistes fuscatus
Polistes fuscatus
Polistes fuscatus
Polistes fuscatus
Polistes fuscatus
Polistes fuscatus Polistes fuscatus Polistes fuscatus
Polistes fuscatus

Taxonomic note. The separation of the hypervariable P. fuscatus from related species remains the greatest taxonomic problem of the northeastern Vespidae fauna. Colour patterns of P. fuscatus are strongly influenced geographically, as in many other Vespidae, and have resulted in the description of many questionable subspecies. Besides geographic variation individual variation is also extremely pronounced. What makes the recognition of P. fuscatus especially challenging is the fact that different parts of the body can follow different colour trends, e.g., the extent of yellow markings can vary independently on head, meso- and metasoma (in most other Vespidae xanthic or melanic tendencies affect all parts of the body in the same direction). The individual distinctiveness of colour patterns in P. fuscatus facilitates recognition of nestmates, and apparently reduces aggressive interactions between individuals (Tibbetts 2002). There is evidence that the social structure of Polistes colonies selects for individual distinctiveness and phenotypic diversity (Tibbetts 2004).
Females of P. fuscatus intergrade with both P. metricus and P. bellicosus, two very differently patterned species. Even though males of these species can be identified without problem there seem to be no reliable morphological characters that separate females. Their identification using colour patterns is not always possible, and it appears that extreme forms of P. fuscatus can show patterns that are indistinguishable from extreme forms of the other two species. The boundaries between the three species as drawn here are therefore tentative.

Species recognition. The male is easily distinguished from other members of the P. fuscatus-group by the complete darkening of the (3–)4–5 apical flagellomeres (including ventral and anterior surface, apex of flagellomere XI sometimes paler). In other species only the dorsal surface of the apical flagellomeres is darkened whereas tyloids and the anterior surfaces are essentially the same light colour (yellow-orange) as the basal flagellomeres. Females from northern localities (including the vast majority of Canadian specimens) are easily identified by the largely black colouration of the whole body (with or without well-developed yellow markings). Problematic are many specimens from the southern half of the range, where the extent of ferruginous markings is often much increased. Females with ferruginous head and mesosoma, dark metasoma and reduced yellow markings resemble P. metricus, whereas females with largely ferruginous body and well developed yellow markings resemble P. bellicosus. The differences are discussed under these species.

Variation. Fore wing length 11.5–17.0 mm, usually above 13.0 mm (♀♀), 11.0–17.0 (♂♂). Female. Extent of ferruginous areas extremely variable, generally increasing from northern to southern latitudes. Largely black northern forms have at least the following body parts ferruginous: small areas on mandible, postocular spot, scape ventrobasally and ventrodistally, flagellum ventrally, small areas on fore and mid femora, most of fore tibia, mid tibia and tarsi. Extremely ferruginous specimens (occurring rarely in the area covered by the Atlas but more commonly further south) are nearly entirely ferruginous, excluding the following black areas: mark around ocelli, dorsoapical spot on scape, upper surface of flagellum, median stripe of scutum, scrobal furrow and dorsal groove of mesopleuron, narrow stripes along some sutures of mesosoma (e.g., scutum – scutellum; metapleuron – propodeum); spot in central groove of propodeum ventrally, small medial spots on metasomal terga 1–3, spots on all coxae. The extent of yellow areas is also very variable. Yellow markings are often well-developed in Canadian specimens but sometimes also in extensively ferruginous-marked specimens from southern localities. Richly marked specimens show the following yellow markings: most of mandible, clypeus ventrally and laterally, lower inner orbits, transverse spot(s) above antennae, postocular spot(s), pronotum along carina and posterior margin, dorsal mesopleural spot and small ventral spot just above mid coxa, anterior fasciae on scutellum and metanotum, metapleural ridge and narrow adjacent areas, pair of longitudinal stripes on propodeum, rarely additional pair of longitudinal stripes or spots on lateral portions of propodeum, propodeal valvula, apical fasciae on terga 1–5 and sterna 2–5, small lateral spots on tergum 1, sometimes discal spots on tergum 2, markings on mid and hind coxae, small areas on all femora and tibiae, dorsal surface of basal segments of tarsi. When very restricted, yellow markings are at least present on the following: pronotal hind margin (often obscure), propodeal valvula, knees of legs, basal segments of tarsi. Male: Variation similar to female but the following always yellow: mandible except apical margin, clypeus, frons up to level of upper margin of ocular sinus, lower gena, ventral surface of antenna from scape to about flagellomere 6 (often suffused with orange), ventral surface of mesopleuron, anterior surface of all coxae (sometimes only small spot on hind coxa), ventral surface of fore femur, anterior surface of mid and hind femur, apical fasciae of sterna 2–5 (sometimes incomplete on 2 or 5), and basal spot on sternum 2. In addition to the yellow markings present in the female the following may be present: ventral corners of pronotum behind carina (almost always); metapleuron ventrally, very rarely also tiny spots on terga 3 and 4, and sternum 1.

Distribution. Canada: NS, PE, QC and ON (Richards 1978, Starr 1991), apparently newly recorded for NB (photographic record, Bugguide); according to Starr (1991) probably also in MB and SK (records not clearly distinguished from P. aurifer, see below). Eastern U.S.: south to FL, west to NE and TX; Bermuda, Jamaica, Barbados, introduced to Cape Verde Is. and Ascension I. (Carpenter 1996a). According to Starr (1991) the ranges of P. fuscatus and P. aurifer (formerly considered a subspecies of P. fuscatus) overlap in MB and SK. As some of the characters previously used to separate the two species (such as the presence of yellow spots on tergum 2) are variable in P. fuscatus the western limit of the distribution of P. fuscatus and the eastern limit of P. aurifer need to be re-examined. Borkent and Cannings (2004) erroneously mentioned P. fuscatus as “native to British Columbia” based on misinterpreted distributional information provided by Carpenter (1996a).

Biology. Nests in sheltered areas above or near the ground such as eaves or roofs or below rocks. Prey are mostly caterpillars but also Orthoptera (Krombein 1979). A detailed study of the social biology of this species was done by West-Eberhard (1969).

 

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